Vacuum IG units are known in the art. For example, see U.S. Pat. Nos. 5,664,395, 5,657,607, and 5,902,652, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional vacuum IG unit (vacuum IG unit or VIG unit). Vacuum IG unit 1 includes two spaced apart glass substrates 2 and 3, which enclose an evacuated or low pressure space 6 there between. Glass sheets/substrates 2 and 3 are interconnected by peripheral or edge seal of fused solder glass 4 and an array of support pillars or spacers 5.
Pump out tube 8 is hermetically sealed by solder glass 9 to an aperture or hole 10 which passes from an interior surface of glass sheet 2 to the bottom of recess 11 in the exterior face of sheet 2. A vacuum is attached to pump out tube 8 so that the interior cavity between substrates 2 and 3 can be evacuated to create a low pressure area or space 6. After evacuation, tube 8 is melted to seal the vacuum. Recess 11 retains sealed tube 8. Optionally, a chemical getter 12 may be included within recess 13.
Conventional vacuum IG units, with their fused solder glass peripheral seals 4, have been manufactured as follows. Glass frit in a solution (ultimately to form solder glass edge seal 4) is initially deposited around the periphery of substrate 2. The other substrate 3 is brought down over top of substrate 2 so as to sandwich spacers 5 and the glass frit/solution there between. The entire assembly including sheets 2, 3, the spacers, and the seal material is then heated to a temperature of approximately 500° C., at which point the glass frit melts, wets the surfaces of the glass sheets 2, 3, and ultimately forms hermetic peripheral or edge seal 4. This approximately 500° C. temperature is maintained for from about one to eight hours. After formation of the peripheral/edge seal 4 and the seal around tube 8, the assembly is cooled to room temperature. It is noted that column 2 of U.S. Pat. No. 5,664,395 states that a conventional vacuum IG processing temperature is approximately 500° C. for one hour. Inventors Lenzen, Turner and Collins of the '395 patent have stated that “the edge seal process is currently quite slow: typically the temperature of the sample is increased at 200° C. per hour, and held for one hour at a constant value ranging from 430° C. and 530° C. depending on the solder glass composition.” After formation of edge seal 4, a vacuum is drawn via the tube to form low pressure space 6.
The composition of conventional edge seals are known in the art. See, for example, U.S. Pat. Nos. 3,837,866; 4,256,495; 4,743,302; 5,051,381; 5,188,990; 5,336,644; 5,534,469; 7,425,518, and U.S. Publication No. 2005/0233885, the disclosures of which are all hereby incorporated herein by reference.
Unfortunately, the aforesaid high temperatures and long heating times of the entire assembly utilized in the formulation of edge seal 4 are undesirable. This is especially the case when it is desired to use a heat strengthened or tempered glass substrate(s) 2, 3 in the vacuum IG unit. As shown in FIGS. 3-4, tempered glass loses temper strength upon exposure to high temperatures as a function of heating time. Moreover, such high processing temperatures may adversely affect certain low-E coating(s) that may be applied to one or both of the glass substrates in certain instances.
FIG. 3 is a graph illustrating how fully thermally tempered plate glass loses original temper upon exposure to different temperatures for different periods of time, where the original center tension stress is 3,200 MU per inch. The x-axis in FIG. 3 is exponentially representative of time in hours (from 1 to 1,000 hours), while the y-axis is indicative of the percentage of original temper strength remaining after heat exposure. FIG. 4 is a graph similar to FIG. 3, except that the x-axis in FIG. 4 extends from zero to one hour exponentially.
Seven different curves are illustrated in FIG. 3, each indicative of a different temperature exposure in degrees Fahrenheit (° F.). The different curves/lines are 400° F. (across the top of the FIG. 3 graph), 500° F., 600° F., 700° F., 800° F., 900° F., and 950° F. (the bottom curve of the FIG. 3 graph). A temperature of 900° F. is equivalent to approximately 482° C., which is within the range utilized for forming the aforesaid conventional solder glass peripheral seal 4 in FIGS. 1-2. Thus, attention is drawn to the 900° F. curve in FIG. 3, labeled by reference number 18. As shown, only 20% of the original temper strength remains after one hour at this temperature (900° F. or 482° C.). Such a significant loss (i.e., 80% loss) of temper strength may be undesirable.
As seen in FIGS. 3-4, the percentage of remaining tempering strength varies based on the temperature that is exposed to the tempered glass. For example, at 900° F. only about 20% of the original temper strength remains. When the temperature that the sheet is exposed to is reduced to 800° F., about 428° C., the amount of strength remaining is about 70%. Finally, a reduction in temperature to about 600° F., about 315° C., results in about 95% of the original temper strength of the sheet remaining. As will be appreciated, it is desirable to reduce any temper strength losses as a result of exposing a tempered sheet of glass to high temperatures.
As noted above, the creation of VIG units includes the creation of a hermetic seal that can withstand the pressure applied from the vacuum created on inside of the unit. As also discussed above, the creation of the seal may conventionally involve temperatures of at or above 500° C. These temperatures are required in order to obtain a high enough temperature in order for the frit material used for the seal to melt and form the required seal for the VIG units. As shown above, such a temperature can result in a strength reduction for VIG units using tempered glass.
One conventional solution to sealing glass substrates together is to use an epoxy. However, in the case of VIG units, epoxy compositions may be insufficient to hold a seal on a vacuum. Furthermore, epoxies may be susceptible to environmental factors that may further reduce their effectiveness when applied to VIG units.
Another conventional solution is to use a frit solution that contains lead. As is known, lead has a relatively low melting point. Accordingly, temperatures for sealing the VIG units may not need to be as high for other frit materials, and thus the tempering strength of tempered glass substrates may not be reduced by the same amount required for other frit based materials. However, while lead based frits may resolve the above structural issues, the usage of lead in the frit may create new problems. Specifically, the health consequences to the population for products that contain lead. Additionally, certain countries (e.g., in the European Union) may impose strict requirements on the amount of lead that can be contained in a given product. Indeed, some countries (or customers) may require products that are completely lead-free.
As is known in the art, when a frit or sealing material is disposed onto a substrate, the coefficient of thermal expansion (CTE) of the sealing material may be different than that of the underlying substrate. This may create a CTE mismatch between the two materials. In such situations, as the temperature of the underlying substrate and the sealing material increases/decreases, the materials may respectively expand/shrink at different rates. This may cause structural problems in a product in which the sealing material is disposed (e.g., bound or adhered) against a substrate. For example, the sealing material may end up delaminating from the underlying substrate and causing the product to fail (e.g., as the VIG loses vacuum). As such failure is undesirable, a CTE filler may be added to the sealing material to adjust its expansion rate to bring it closer to (or match) that of the underlying substrate.
For certain applications (e.g., a given frit/substrate combination), an appropriate CTE filler may be known and may simply be added to the frit to obtain a CTE match. However, certain types of frits/glass articles may not have known or acceptable CTE fillers (e.g., a known CTE filler may contain lead above a certain amount), thus making it generally unsuitable for some markets and/or non-compliant with certain standards. Accordingly, it will be appreciated that CTE fillers for certain types of frit material, for example, a vanadium based frit material, may be desirable.
It will also be appreciated that techniques for creating improved seals for glass articles are continuously sought after.
Furthermore, frit materials may sometimes include binder agents that are used to, for example, facilitate binding the various materials that make up the frit. However, in certain instances the materials used in a frit may have a melting temperature that is less than a burn out point for a binder that is used in the frit. In such situations, the incomplete burn off of a binder may result in a porous frit seal, reduced frit to glass bonding due to, for example, carbon contamination in the frit, or other characteristics that may be undesirable for frit based seals.
Accordingly, it will be appreciated that there exists a need in the art for binders, solvents, CTE fillers, etc., that may be used with frit materials, e.g., with frit materials that have a relatively reduced melting point such as vanadium based frits (e.g., VBZ frits).
It also will be appreciated that there exists a need in the art for improved seals and the like that can be integrated with tempered glass units, such as, for example, VIG units. The seals may be designed to allow for reduced temperature sealing such that annealed or tempered glass can be sealed without detrimental impact on the properties of the glass.
In certain example embodiments, a frit material may provide glass to frit bonding sufficient for VIG purposes (e.g., in terms of structural strength). In certain example embodiments, the provided frit may provide proper glass wetting properties. In certain example embodiments, the frit may seal and have structural strength and a homogenous glassy structure to provide an adequate barrier to prevent vacuum degradation in example VIG units over a period of time.
In certain instances, improvements in melt flow may enable improved frit matching to glass expansion and/or increase process tolerances to frit bead variations. Improved wetting and bonding properties of a frit material may increase VIG yield by reducing bonding failures of the frit to the glass. A reduction in crystallization may additionally or alternatively facilitate a selected composition to meeting different heating environments (e.g., an internal seal, an external seal, etc).
In certain example embodiments, a method of making a vacuum insulated glass (VIG) unit is provided. First and second glass substrates are provided in substantially parallel, spaced apart relation to one another, with a gap being defined between the first and second substrates. A material is disposed proximate to the first and/or second glass substrates, with the material comprising at least a frit material and a coefficient of thermal expansion (CTE) material. Energy is applied to the material so as to melt the material at a melting temperature. The CTE material comprises elements that are substantially spherical in form, and said elements are between about 60 and 100 microns in size. The frit material is formed from a base composition includes ˜45-50% (Normalized Mole %) vanadium oxide, ˜20-23% (Normalized Mole %) barium oxide, and ˜19-22% (Normalized Mole %) zinc oxide.
In certain example embodiments, a material is provided. A coefficient of thermal expansion (CTE) material is substantially lead-free. A frit material has a composition that includes: ˜45-50% (Normalized Mole %) vanadium oxide, ˜20-23% (Normalized Mole %) barium oxide, and ˜19-22% (Normalized Mole %) zinc oxide. The material has a first CTE value that is within about 15% of soda lime silicate glass by virtue of the CTE material's composition.
In certain example embodiments, a vacuum insulted glass (VIG) unit is provided. First and second substantially parallel, spaced apart glass substrates are provided. An edge seal is provided around a periphery of the first and/or second substrates to form a hermetic seal therebetween and at least partially defines a gap between the first and second substrates. The gap is provided at a pressure less than atmospheric. The edge seal is formed from the material, at least initially, according to the techniques disclosed herein, e.g., so as to include vanadium, barium, and zinc, as well as at least 4 additives, and a CTE matching material.
In certain example embodiments, a method of making a material is provided. A composition is provided to a holder, the composition comprising ˜45-50% (Normalized Mole %) vanadium oxide, ˜20-23% (Normalized Mole %) barium oxide, and ˜19-22% (Normalized Mole %) zinc oxide. The composition is melted. The melted composition is cooled and/or allowed to cool so as to form an intermediate article. A base frit material is creating from the intermediate article. The base frit material is combined with a CTE filler material that is comprised of particles that are 150-170 mesh and substantially spherical in shape.
In certain example embodiments, a method of bonding a frit material to a glass substrate is provided. The frit material is combined with a CTE material to form a combined material. The combined material is disposed on the substrate. The combined material is heated to a temperature of less than about 400 degrees C. A coefficient thermal expansion associated with the combined material is within 10% of a coefficient of thermal expansion for the glass substrate when heat is applied to the combined material. The frit material includes a composition comprising: ˜45-50% (Normalized Mole %) vanadium oxide, ˜20-23% (Normalized Mole %) barium oxide, and ˜19-22% (Normalized Mole %) zinc oxide.
The features, aspects, advantages, and example embodiments described herein may be combined in any suitable combination or sub-combination to realize yet further embodiments.